A New Solar Metal Sulfate - Ammonia Based Thermochemical Water Splitting Cycle For The Production Of Hydrogen

All sulfur-family thermochemical water splitting cycles (TCWSCs) rely on concentration and decomposition of sulfuric acid for the oxygen evolution step of the cycle. The sulfuric acid decomposition step presents serious materials and catalyst deactivation challenges. Platinum based catalysts are currently the most active for the H2SO4 decomposition, but they deactivate rapidly. To overcome this difficulty metal sulfate based TCWSCs have been developed. However, the metal sulfate based TCWSCs utilize thermal heat input - thus degrading photonic energy. Based upon FSEC\u27s S-NH3 TCWSC, a new family of hybrid photo/thermo-chemical water splitting cycles is introduced in this paper that employs the quantum portion of the solar spectrum for the production of hydrogen and the thermal energy (i.e. IR) portion of solar radiation for generating oxygen. FSEC\u27s metal sulfate - ammonia (MSO 4-NH3) hybrid photo/thermochemical water splitting cycles are represented by the following reactions: \[ \begin{array}{llc} {\rm SO}-2 ({\rm g}) + 2 {\rm NH}-3 ({\rm g}) + {\rm H}-2 {\rm O}(1) \to ({\rm NH}-4)-2 {\rm SO}-3 ({\rm aq})\quad & ({\rm chemical\ absorption})\quad & 25\circ {\rm C}\\[4pt] ({\rm NH}-4)-2 {\rm SO}-3 ({\rm aq}) + {\rm H}-2 {\rm O} \to ({\rm NH}-4)-2 {\rm SO}-4 ({\rm aq}) + {\rm H}-2 ({\rm g})\quad & ({\rm solar\ photocatalytic})\quad & 80^\circ {\rm C}\\[4pt] {\rm x}({\rm NH}-4)-2 {\rm SO}-4 + {\rm M}-2 {\rm O}-{\rm x} \to 2 {\rm xNH}-3 + {\rm M}-2 ({\rm SO}-4)-{\rm x} + {\rm xH}-2 {\rm O}\quad & ({\rm solar\ thermocatalytic)\ quad & 500^\circ {\rm C}\\[4pt] {\rm M}-2 ({\rm SO}-4 )-{\rm x} ({\rm s}) \to {\rm xSO}-2 ({\rm g}) + 2 {\rm MO} ({\rm s}) + ({\rm x} - 1) {\rm O}-2 ({\rm g})\quad & ({\rm solar\ thermocatalytic})\quad & 1100^\circ {\rm C} \end{array} \] Where, M = Zn, Mg, Ca, Ba, Fe, Co, Ni, Mn, Cu. Chemical equilibrium calculations for the reaction between ZnO and (NH4) 2SO4 indicate that both ZnSO4 and ZnO.2ZnSO4 can form as the stable reaction products. A series of thermogravimetric/differential thermal analyses/mass spectrometric (TG/DTA/MS) experiments has been carried out to determine the exact nature of all ZnO + (NH4)2SO4 reaction products. Results obtained to date are presented and discussed. © 2009 World Scientific Publishing Co. Pte. Ltd